Cold cathode discharge device and method of manufacture



W. L. MEIER March 9, 1954 COLD CATHODE DISCHARGE DEVICE AND METHOD OF MANUFACTURE Filed Sept. 6, 1951 FIG.2

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pumflm FBGE Patented Mar. 9, 1954 COLD CATHODE DISCHARGE DEVICE AND METHOD OF MANUFACTURE Wilber L. Meier, Chatham, N. J.

Application September 6, 1951, Serial No. 245,291

7 Claims. 1

This invention relates to cold cathode gaseous discharge devices, and has particular reference to an electrode structure which may be degassed and purified during the process of exhausting and filling.

Many types of cold cathode gaseous discharge devices utilize a coated cathode to provide the proper discharge characteristics. One well known method of obtaining a desirable coating consists in coating the cathode with a mixture of barium and strontium carbonates to which a small percentage of calcium carbonate may be added. During the exhaust process the carbonates are heated and decompose, changing to metallic oxides. It is also necessary to raise the temperature of all the electrodes to bake out occluded gas and to eliminate films of water or other liquids. One method of heating the electrodes comprises filling the tube to a low gas pressure and passing an electrical discharge between the electrodes of such intensity as to generate the required temperature. This method eliminates a considerable amount of occluded gas, but sometimes the heat is not evenly distributed, some electrodes may get hotter than others, and the carbonates on some portion of the cathode may not be completely decomposed, or the oxides may be evaporated from that portion of the cathode which attained the highest temperature.

Another method of heating the electrodes comprises the use of a high frequency inductance coil surrounding the tube envelope. This method works well but is expensive, and the current through the coil must be adjusted for each tube.

When a large number of tubes are being exhausted and filled on one pump manifold, the adjustments necessary to assure equal heating for each tube consumes time and slows up the manufacturing rate.

One of the objects of this invention is to provide an improved gas discharge device and an improved method of exhausting cold cathode discharge devices which avoids one or more of the disadvantages and limitations of prior art arrangements and methods.

Another object of the invention is to shorten the exhaust time of a gas discharge device by quickly disposing of the occluded gases in the discharge electrodes and uniformly decompose the carbonates in the cathode coating.

Another object of the invention is to produce gas discharge devices which are more uniform in their voltage and current characteristics.

Another object of the invention is to provide charge tube may be raised to a uniform high temperature during the exhausting and filling operations.

The invention comprises a cold cathode with a heater element which can be operated to heat the electrode during the exhaust process to drive 01f occluded gases and decompose the cathode carbonate coating. The invention also includes a temporary connection between electrodes for heating them by the conduction of electric current. After the initial exhaust operation the connecting wires are burned out by an excess current pulse. The invention is suitable for gas discharge tubes having any number of electrodes but can be applied with especial advantage to small, two-electrode lamps which are used as circuit elements in communication equipment and in electronic calculators.

For a better understanding of the present invention, together with other and further objects thereof, reference is made to the following dedescription taken in connection with the accompanying drawings:

Fig. 1 is a cross sectional view of a cold cathode gas discharge device having a cathode heater for operating during the exhaust operation.

Fig. 2 is another cross sectional view of an alternate construction showing a conductive wire connecting the two electrodes.

Fig. 3 is a cross sectional view of a cold cathode gas discharge device for use with an alternating current supply and having two similar electrodes, both with internal heaters.

Fig. 4 is a cross sectional view of a two-electrode cold cathode gas discharge device having both electrodes made of thin wires and having a connecting wire between the upper ends of the electrodes.

Fig. 5 is a view similar to Fig. 2 but showing a structure suitable for degassing both electrodes and having only two lead-in conductors.

Fig. 6 is a cross sectional view of a two-electrode discharge device in which the cathode is heated by the passage of current through it during the exhausting operation.

Referring now to Figs. 1 and 2, an envelope [0 encloses all the electrodes which are connected to lead-in conductors ll, l2, and i3. A reentrant type seal is shown in these figures, but any type of seal for holding the lead-in conductors may be used. The cathode I4 is a hollow cylindrical tube welded to lead-in conductor H and may be made of nickel or any other suitable conductor.

The anode for this type of tube may be a single straight wire I5. If it is desired to heat the anode by passing current through it, a connecting wire I6, shown in Fig. 2, is employed. For heating the cathode during the exhaust operation, a heater element I1 is mounted inside the hollow cylinder I4 and connected to the cathode lead-in conductor II and the lead-in conductor I2. If a thin wire is used for the anode it may be necessary to mount an insulator washer I9 near the top of the tube. This washer, which may be a mica disk, keeps the electrode spacing constant. This heater element is made from uniform drawn tungsten wire, and when multiple exhausting is contemplated, all tubes are supplied with heaters having the same length. In order to avoid short circuiting between portions of the heater or to the conducting walls of the cathode, the heater is coated with a non-conducting substance.

The discharge device shown in Fig. 1 is exhausted as follows: After sealing the exhaust tubes to the pump manifold and evacuating to a lower pressure current is passed through the heater element I! by the use of lead-in conductors II and I2. All the heaters on the manifold may be connected in series to insure that the heating current is the same in all the tubes. The heater current is adjusted by slowly increasing its value to obtain the proper rate of decomposition of the carbonates. The cathode is maintained at a high temperature until a vacuum gauge in the pumping system indicates no more gas is being given on" by the cathode. At this time a small amount of gas may be put into the tube and a steady operating voltage applied to conductors II and I3 to start a gaseous discharge in the tube and partly degas anode I5. After a short ageing discharge the heater current is turned off and the tubes filled with the operating gas and the device is then sealed off. The heater I! may be left intact since its presence has no influence on the normal use of the tube as a gas discharge device. To make sure that the heater element is not used after the exhaust operation that part of the conductor I2 which extends beyond the seal may be cut oii.

The discharge device shown in Fig. 2 is exhausted in a manner similar to that described above but in addition, while degassing the oathode, a voltage is applied to lead-in conductors I I and I3 and current is sent through the cathode,

the connecting wire I6, and the wire anode I5.

It should be noted that a heavy portion I8 of anode I5 is provided at the base so that the temperature of this point is not sufficient to cause the glass to crack. By the proper choice of materials,

such as a copper covered connecting wire I6 and a bare tungsten wire anode I5, the anode may be raised to a temperature which will degas it in a short time. When the degassing process is complete, current is cut off from the anode and wire I6 until they both become cool, then a short high current pulse is applied to the same elements. This pulse melts the connecting wire I6 because, due to the short time interval, the heat cannot be radiated and the temperature increases to a value which is above the melting point. The tungsten anode is not harmed because its cold resistance is low and its melting point is high. After the connecting wire I6 has been eliminated, the usual exhaust and sealing operations may be concluded.

The discharge device shown in Fig. 3 is adapted to be used with alternating current and represents a design suitable for very small indicator lamps. An envelope I0 encloses two similar electrodes 20 and 2I which are connected to lead-in conductors 22 and 23. The electrodes are hollow and a small heater element 24 is mounted inside each one to heat it to degassing temperature during the exhaust operation. The heater elements are connected at their upper ends to the electrodes while their lower ends are threaded through an insulating spacer 25 and joined together. The heater elements may be made of tungsten wire with an insulating coating and the connecting wire below spacer 25 can be the same size tungsten wire without the coating. This construction permits the operation of heaters in both electrodes without an extra lead-in conductor.

The method of degassing this tube (Fig. 3) is similar to the examples described above. Heating current, applied at conductors 22, 23, heats the elements 24 and electrodes 20, 2I. After degassing, the heater elements are allowed to cool off, then an increased voltage is applied to the conductors 22, 23, and that part of the tungsten filament below the spacer 25 will burn out and leave the electrodes disconnected from each other and ready to function in the normal manner.

The gas discharge lamp shown in Fig. 4 contains two similar tungsten wire electrodes 21 and 28 connected to lead-in conductors 30 and SI at one end of the envelope I0, and joined by a dispossible copper connecting wire 32 at the other end. An insulating washer 33 holds the upper ends of the wire electrodes in place. Because of its obvious symmetry, this design can be used on alternating current.

The method of exhausting and filling is the same as that employed in the previous example. Because wires 21 and. 28 are the same size and are made of the same material, they will be heated to the same temperature when current is applied to terminal wires 30 and BI. The disposable connecting wire 32 is melted by the application of a strong current pulse when the electrodes have cooled.

The gas discharge device shown in Fig. 5 is an alternate structure and similar to the tubes shown in Figs. 2 and 3. It has only two lead-in conductors and 4 I. A hollow cathode 42 and a wire anode 43 are connected to the lead-in conductors and are held in position by a spacer 44. A heater element 45 is mounted within the hollow cathode with its upper end connected to the anode and its lower end connected to lead-in conductor 40. During the degassing process current passes through the heater element and the wire anode from a battery 52 controlled by a vari able resistor 53 and a switch 54. This structure is not as flexible as some of the examples described above since the relative sizes of wire in the heater element and the size of the anode must be carefully chosen. Both the cathode and anode should reach degassing temperatures with the same current, otherwise one electrode may be too cool to degas properly. After the degassing process the connection is broken above the spacer 44 by the method described above. In order to insure melting of the heater wire at the proper point, only that part of the wire which is above the spacer is. left bare. All other portions are coated with the usual insulating coating.

The gas discharge device shown in Fig. 6 comprises an envelope II) which encloses a wire an ode 4'! and a strip cathode 48. The cathode is formed from a. thin ribbon of nickel or other suitable material and is coated with emissive material. It is mounted on two. lead-in conductors and 5|, only one of which is used when the device is employed as a circuit element. During the exhaust process, current applied at conductors 5D and 5| heats the cathode strip 43 and degasses the area on which the emissive material has been desposited.

From the above described examples it will be evident that other combinations of heaters and electrodes may be employed during the exhaust process in order to completely degas the electrode surfaces and produce tubes of uniform quality.

While there have been described and illustrated specific embodiments of the invention, it will be obvious that various changes and modifications may be made therein without departing from the field of the invention which should be limited only by the scope of the appended claims.

I claim:

1. A cold cathode gas discharge device containing components for aiding in degassing electrodes during the evacuation and filling process comprising; an enclosing envelope of glass; a tubular cathode and an anode within the envelope; a coating of electron emissive material on the outside of the tubular cathode; said cathode containing a resistor element inside the tube, one terminal of which is conductively secured to the cathode, the other terminal of which is secured to the anode; means for heating the resistor element to a predetermined temperature by the application of a source of electric current to the cathode and the anode; and means for disconnecting the conductive connection between anode and cathode by the application of a source of electric current to said electrodes of sufi'icient intensity to burn out the conductive connection.

2. A cold cathode gas discharge device containing components for aiding in degassing electrodes during the evacuation and filling process comprising; an enclosing envelope of glass; a tubular cathode and an anode within the envelope; a coating of electron emissive material on the outside of the tubular cathode; said cathode containing a resistor element inside the tube, one terminal of which is conductively secured to the cathode, the other terminal of which is connected to the anode by a disposable conductor; means for heating the resistor element to a predetermined temperature by the application of a source of electric current to the cathode and the anode; and means for vaporizing the disposable conductor by the application of a source of electric current to said electrodes of substantially greater intensity than that needed to heat the resistor.

3. A cold cathode discharge device containing components for aiding in degassing electrodes during the evacuation and filling process comprising; an enclosing envelope of glass; a tubular cathode and an anode within the envelope; a coating of electron emissive material on the outside of the tubular cathode; said cathode containing a resistor element inside the tube, one terminal of which is conductively secured to the cathode, the other terminal of which is secured to the normally free end of the anode; means for heating both the anode and the cathode to a predetermined temperature by the passage of current through the anode and the resistor; and means for disconnecting the resistor from the anode by the passage of a current pulse through said anode and resistor of substantially greater intensity than that needed to heat the resistor.

4. The method of degassing a cathode in a gaseous discharge device containing electrodes within a glass envelope which receive no heat from an external source during normal operation, said method comprising; heating the cathode to a predetermined temperature to drive olT occluded gas molecules during the process of exhausting the envelope by the passage of electric current through a resistor which has one terminal connected to the cathode and the other terminal connected to an anode, applying an electric pulse to the resistor to dispose of the connection to the anode, filling the envelope with gas, and then sealing the glass envelope.

5. The method of degassing a cathode in a gaseous discharge device containing electrodes within a glass envelope which receive no heat from an external source during normal operation, said method comprising; heating the cathode to a predetermined temperature to drive off occluded gas molecules and to condition a coating of electron emissive material on the cathode surface, said heating performed by the passage of electric current through a resistor which has one terminal connected to the cathode and the other terminal connected to one of the other electrodes; applying an electric pulse to the resistor to dispose of the connection to the electrode; filling the envelope with gas; and then sealing the glass envelope.

6. The method of degassing a cathode in a gaseous discharge device containing electrodes within a glass envelope which receive no heat from an external source during normal operation, said method comprising the following steps; heating the cathode to a predetermined temperature to drive oiT occluded gas molecules during the process of exhausting the envelope by the passage of current through a resistor, applying an electric pulse to the resistor which disposes of part of the resistor, filling the envelope with gas, and then sealing the envelope.

'7. The method of degassing a tubular cathode in a gaseous discharge device containing electrodes within an envelope which receive no heat from an external source during normal operation, said method comprising the following steps; heating the cathode to a predetermined temperature to drive off occluded gas molecules during the process of exhausting the envelope by the passage of current through a resistor mounted within the tubular cathode, applying an electric pulse to the resistor which disposes of part of the resistor, filling the envelope with gas, and then sealing the envelope.

WILBER. L. MEIER.

References Cited in the file Of this patent UNITED STATES PATENTS Number Name Date 1,722,468 Hunter July 30, 1929 1,935,939 Case Nov. 21, 1933 2,003,344 De Boer June 4, 1935 2,155,237 Perrott Apr. 18, 1939 2,236,859 Vandergrift Apr. 1, 1941 2,330,848 Smith Oct. 5, 1943 

